I know I'm tiring you with this answer, but this is yet another feature planned for the upcoming release.
In the meantime, I suggest you use a different approach instead of (the somewhat hackish) AdditionalAttributes:

Yes, I'll have to add an event-callback after the grid finished initial rendering (and not in subsequent refreshes).
In the mean time you could use a first time flag in the initGridToolbar. (I know I know...)